Meeting Abstract
Aquatic insects are widely used as indicators in freshwater ecosystems, but we know little about how temperature dictates performance and limits within and across species. Oxygen limitation (the mismatch between oxygen supply and demand) has been proposed as the primary mechanism that determines thermal limits, but the concept has not been adequately assessed in aquatic insects. We used rearing studies to establish thermal reaction norms in mayfly Neocloeon triangulifer in combination with respirometry studies to ask if the oxygen limitation hypothesis is supported in this species. Larvae were reared from newly hatched eggs to adulthood at 2 °C degrees interval from 14-28 °C, though 30 °C prevented larvae from reaching adulthood. This species follows the temperature size rule, with warmer temperatures resulting in smaller, less fecund individuals. Respiration rates measured from larvae reared across different temperatures show a positive relationship between oxygen consumption and larvae weight. This positive relationship becomes stronger with increasing temperature, suggesting there is a cost of growing bigger at higher temperatures. However, there is no indication that oxygen is limiting to 30 °C larvae. In fact, we observed a 2-fold increase in respiration rates between ecological (30 °C) and acute thermal limits (37 °C in our experiment), suggesting that larval oxygen consumption is commensurate with demand at ecological (chronic) thermal limits. Increasing metabolic costs appear to limit body size in thermally challenged mayflies, but oxygen does not appear to be limiting at chronic thermal limits.
